1. Field of the Invention
This invention relates to a flash unit in which light is emitted by discharging electrical energy accumulated at a main capacitor to a discharge tube, and more particularly to a power source circuit which is provided in the flash device for charging the main capacitor with a predetermined value of electrical energy.
2. Description of the Prior Art
Commonly, a power source circuit for a flash unit is arranged such that a switching element, e.g. a thyristor or the like, is connected between a battery and a main capacitor to charge the latter with electric energy. When the charge voltage of the main capacitor reaches a predetermined voltage value required for light emission by a discharge tube, a signal for making the switching element conductive is removed to make it nonconductive. Thus, the main capacitor is charging operation is stopped so that it is charged up to the predetermined value. In the conventional power source circuit of this type, this operation stops when the charge voltage of the main capacitor reaches the predetermined value. After that, however, the switching element may to be turned on again by noise or the like. This causes the main capacitor to be further charged. Thus, the main capacitor is occasionally damaged by overcharging.